Damp in the extension - sealing a drain

[jonjay48]

I have a 4" pipe coming into the extension, the top of which that comes in ~6" below the surface, then runs down the length of the extension and out the back.

the extension was built over an old garage, and the pipe runs along a concrete slab that I can only assume was the original foundations of the garage that the extension replaced.

Where the pipe comes in, since it is below the surface outside, there is damp coming in, and this then ends up sitting on the contrate slab - making the whole area under the floor very damp. (literally glistening on the surface of the concrete slab)

I've checked the pipe, and I'm 99% sure that its not leaking, so I guess the damp is coming in vis the large gap around the pipe (when you look down the length, the pipe goes under a small lintel, has a gap of about 2" on either side, and then after the outside wall goes directly into soil outside)

Is there anyway I can seal round the pipe?

Should I drill lots of holes in the concrete slab to allow water to soak away?

sorry for long question!
Thanks, Jon

 

[noseall]

are you saying that there is surface water forming on the inside floor of the building? or is it condensation? how mutch water?

when was the extension built?

many buildings are constructed with a drain pipe running below. these are lintelled over with no particular seal around them. the dpm should resist any moisture

 

[jonjay48]

The extension was built in 2004 - over the old garage. The concrete floor that is damp is very old - I'm guessing when the house was built (1970s), and so has no dpm underneath

the concrete floor has a lot of rubble over it (in places a foot deep), and in most areas this is dry.

the joists are then about 6" about the rubble layer, and in parts these are damp as well.

I'm not sure where the moisture is coming in, but the pipe area (all along its length) is moist, and when I dug away the rubble is was wetter and wetter until I reached the concrete slab (where it was glistening).

I'm almost certain the pipe is not leaking, since I had a hose running into it for some time, and I'd slid bin liners underneath it to see if this got damp - which it didn't.

I'm wondering if the moisture is coming in along the pipe on the outer surface, seeping from the soil outside?

not sure!

 

[noseall]

I'm wondering if the moisture is coming in along the pipe on the outer surface, seeping from the soil outside?

not sure!

quite likely as water will follow the easiest path. easiest being disturbed ground.

concrete or even a sand and cement mortar plug will resist low water pressure.